The present invention relates to an interface for a maintenance system used in conjunction with a process instrumentation system. More specifically, the invention relates to an interface used for maintaining and configuring smart devices. Even more specifically, the invention relates to an interface that may safely be used to maintain and configure smart devices where such smart devices are located in hazardous areas.
Modern process control systems often utilize field devices for monitoring and controlling various aspects of a process. These field devices can include level transmitters, mass flow meters, tank gauges, pressure transducers, temperature transducers, or other similar devices. Typically, these field devices output 4-20 mA signals which are operated upon to provide information regarding a process. An example of such a field device is a pressure transducer located in a storage facility filled with gasoline that periodically outputs signals that are operated upon to determine the pressure in the storage facility.
Widely used field devices that are commonly referred to as "smart transmitters" (i.e. smart field devices) are often equipped with microprocessors. These microprocessors perform two important functions: (1) process measurement, and (2) calibration, adjustment, and maintenance of the smart transmitter to within desired levels of operation. Collectively, the operations of calibration, adjustment, and maintenance shall be referred to hereinafter as "maintenance." The maintenance function is the focus of the present invention.
The smart transmitters mentioned above are usually connected to what is known in the art as a Distributed Control System (DCS), a Programmable Logic Controller (PLC), a Personal Computer (PC), or other similar control device. Collectively, DCSs, PLCs, PCs, and other similar devices shall be referred to herein as "control systems." It is common in the field of process instrumentation to have the connection of any particular smart transmitter to a control system typically be in the form of a 4-20 mA loop in which power to energize the smart transmitter is supplied from the control system.
Typically, a control system primarily receives and processes the 4-20 mA signals that are transmitted from the smart transmitters over the 4-20 mA loops. In this fashion, data about the process that is being controlled or monitored can be collected and analyzed. Additionally, typical control systems can be equipped with facilities for providing for the maintenance of the smart transmitters (i.e. the calibration, adjustment, and maintenance of smart transmitters). Control systems equipped with facilities for providing for the maintenance of smart transmitters often achieve such operations by incorporating proprietary systems and protocols for the transmission of digital maintenance data to and from the microprocessors found in the smart transmitters. With these types of control systems, only smart transmitters manufactured by the manufacturer of the control system can be used for process control due to the proprietary nature of the systems and protocols involved.
Several problems are associated with using control systems that incorporate proprietary maintenance systems and protocols for the communication of maintenance data, to and from smart transmitters. Initially, communication is commonly not done over the connection forming the 4-20 mA control loop. Instead, separate wiring systems need be installed, thus increasing maintenance cost and complexity.
Another problem is that proprietary protocols can dictate control system and smart transmitter manufacturer uniformity. That is, a plant or process facility that uses a proprietary protocol based control and maintenance system may be restricted in its ability to acquire process control equipment manufactured by differing vendors possibly rendering the plant or process facility vendor or product line dependant. Various tangential problems are associated with being vendor or product line dependant including the possibility of having to pay higher and higher prices for process control equipment due to market monopolies. Even more, being vendor or product line dependant can result in restricting a process facility's operations based on the availability and selection of process control equipment. For example, when a plant or process facility seeks to perform certain tasks, such a facility may have to re-equip to meet changing demands in running and controlling processes. Such re-equipping, in addition to possibly being impracticable, can be quite costly.
Yet another problem can be seen where a process facility, including those involving hazardous areas, may utilize several hundred, or more, smart transmitters to measure and evaluate particular processes. In these situations, wiring of the smart transmitters to both the control system and the maintenance system can become quite complicated, problematic, and costly. The wiring problem is compounded where the control system and the maintenance system each require separate wiring systems. Even in light of these wiring problems, there have been no available centralized wiring harnesses that enable users to simply and easily gain wiring access to the control and maintenance signals communicated to and from the smart transmitters.
Another problem with providing for maintenance of smart transmitters is seen where there is failure of the maintenance system in the context of control systems that incorporate maintenance systems. When the maintenance system in these systems fail, the entire control system may need to be shut down thus requiring any of the processes that are being controlled by the control system to come to a halt as well. Termination of processes can be costly as well as impracticable. Even more, where a process must be halted, it may be necessary to re-start the process once the maintenance system is again operational.
The above-mentioned problems are compounded where there is a requirement of intrinsic safety. In applications requiring intrinsic safety, smart transmitters are used in hazardous areas and the control and maintenance stations reside in a non-hazardous area. Such applications include, for example, gasoline manufacturing facilities and the like. In these applications, it can become quite difficult to adjust, calibrate, and maintain smart transmitters during a process due to the hazards involved. While intrinsically safe circuits (e.g. circuits utilizing opto-isolators, transformers, for examples) are often utilized to protect against the hazards involved in monitoring and measuring processes in hazardous areas, the range of products available for such intrinsic safety applications is quite small. Even more, these intrinsic safety circuits fail to lend themselves to easily and economically allow for maintenance of smart transmitters.
Another problem associated with currently used process instrumentation devices is seen where the control system protocols, whether proprietary or not, are incompatible with commercially available smart transmitters. Control systems within these process instrumentation systems often cannot interface with the smart transmitters and thus require the use of an additional maintenance system. These problems are compounded when intrinsic safety is required.
The above-listed problems have led the Inventors to invent solutions that are practical and economical and which are defined in the appended claims.